Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, the deposited layer is often etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, can become increasingly non-planar. This non-planar surface may present problems in the photolithographic steps of the integrated circuit fabrication process. Therefore, there is often a need to periodically planarize the substrate surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically includes mounting a substrate on a carrier or polishing head using a load cup assembly. The exposed surface of the substrate is placed against a rotating polishing pad. The polishing pad may be either a “standard” or a fixed-abrasive pad. A standard polishing pad has a durable roughened surface, whereas a fixed-abrasive pad typically has abrasive particles held in a containment media. The polishing head provides a controllable load, i.e., pressure, on the substrate to push it against the polishing pad. A polishing slurry, including at least one chemically-reactive agent, and abrasive particles, if a standard pad is used, is supplied to the surface of the polishing pad.
The polishing head can undergo periodic maintenance in which the head is disassembled, worn parts replaced and then reassembled. Prior to returning the head to polishing additional wafers, the refurbished head can be tested at a test station to determine whether the head operates properly before using it on expensive wafers or other semiconductor substrates.